JPH02162569A - Signal identifier - Google Patents

Abstract

PURPOSE: To identify the presence and absence of writing by providing an encoding means and a means for forming the sequence of the corresponding notch in the given signal and deciding the existence of a code signal in any of the given signals. CONSTITUTION: An audio signal is supplied to notch filters 301, 303 through an A/D converter 307, digitized and supplied to the control branch of encoder including a masking filter 305. The output of the filter 305 is supplied to a multiplier 311, to which the output of a code frequency generatorr 211 is also supplied, through a rectifier 309 and connected to an adder 313. When this encoder is used, the adder 313 generates a desired encoded audio signal. The filters 301, 303 form a series of notches in the audio signal in a frequency band determined by a sequence generator and encoded to a proper code signal. Consequently, a decoder system is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal identification device, and more particularly to a device in which a code is superimposed on a signal so that signals can be sequentially identified. Such devices have special uses, such as when making sound recordings, to provide the recording industry with information identifying the original of the recording, the copyright holder of the recording, the presence or absence of copyright fees payable, etc.

European Patent Application No. 02450 filed by the applicant
No. 37 describes a device for forming an identification code when recording a soundtrack, and this device includes:
An encoder circuit is provided for removing two predetermined frequency bands from the audio signal to form notches in the signal. The encoder circuit inserts into these notches a signal in the form of a suitable identification code, which code signal consists of a pulse at the center frequency of the notch, and the value of each digit of the code sequence is It is represented by one frequency, and different values of each digit are represented by other frequencies.

Such devices allow codes to be inserted into high fidelity audio signals in an inaudible but recoverable manner using digital or analog techniques. However, by using a narrowband notch filter that operates at the same frequencies used in the original recording process, this device makes it difficult for potential fraudsters, such as home copiers, to filter out the codes. This poses a problem of protection.

One object of the invention is to provide a device suitable for generating identification codes during soundtrack recording that are more difficult to filter out without deteriorating the audio signal.

According to one aspect of the invention, a signal identification device is provided that includes encoding means. The signal identification apparatus includes means for selecting a variable sequence of frequency bands from a plurality of different predetermined frequency bands within the bandwidth of a given signal, and means for selecting a variable sequence of frequency bands from a plurality of different predetermined frequency bands within a given signal bandwidth; means for subtracting from the signal to form a corresponding sequence of notches in said given signal and inserting into said notch a sequence of each code signal having a frequency within the bandwidth of said notch undergoing insertion; and decoding means for determining in which of the signals given λ a code signal is present.

In the device according to the invention, since the notch frequency bands are spread over a wide range of the signal spectrum, any attempt by a fraudster to remove or block all possible notch frequency bands at the same time will be avoided in the audio signal. This will result in significant distortion of the image. Although it is possible to detect the presence of individual notches and filter out data that falls within each notch's frequency band, sophisticated signal processing means are at least beyond the capabilities of the average home copier. would be necessary. Furthermore, although the notch will move around the signal spectrum in a pseudo-random manner, the presence of a notch will be more difficult to detect audibly or using electronic test equipment if the signal is an audio signal.

In a preferred embodiment according to the invention, at least 3
There are two different predetermined frequency bands, and each code signal has a frequency within the two different predetermined frequency bands.

According to the invention, there is also provided an encoding device for coding a given signal, which encodes one of the frequency bands from a plurality of different predetermined frequency bands within the bandwidth of the given signal. means for selecting a variable sequence; means for removing a selected sequence of frequency bands from said given signal to form a corresponding sequence of notches in said given signal; and said notches undergoing insertion. means for inserting into said notch each sequence of code signals having a frequency within a bandwidth of .

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is a device designed to form an identification code signal in a high fidelity music soundtrack and is described in the aforementioned European Patent Application No. 0245037 filed by the applicant. It is applied to

Referring first to FIG. 1, the apparatus performs coding based on the selection of three different combinations of notch frequency bands selected from among all six different notch frequency bands within the frequency spectrum of a music track. Designed to use signals. As shown in FIG. 1, the above six frequency bands are located in the middle between each note from E3 to As4. Therefore, the number of combinations of two frequency band bears is 15.

However, in order to simplify the device by reducing the number of decoders ultimately required to decod the encoded audio signal, in this embodiment, for example, the A pair in the figure,
Like B-bear and C-bear, the number of allowed combinations is limited to three.

This number 3 is the minimum number of combinations to ensure that each notch frequency band is used at least once.

Referring to FIGS. 2 and 3, a random sequence generator 201 is used to select which of the possible combinations A, B, and C of the frequency band bears has a coding signal, and the two switch 203.205
operate. random sequence generator 20
The filter coefficient memory 207 that operates under the control of
The digital signal processing (DSP) chip in encoder 209 is loaded with the appropriate software signals to center the frequencies of the selected frequency band, such as 2713 Hz and 3228 Z for the A pair, as shown in FIG. Program the two notch filters shown as 301 and 303. The filter coefficient store 207 is also useful for programming a masking filter, shown as 305 in FIG. Code frequency generator 211 responsive to random sequence generator 201 includes two notch filters 301 .
A binary coding pulse is generated at a center frequency of 303. In this case, the 2713 Hz pulse marks a space or zero in each data bit of the coding signal, and the 3228 Hz pulse marks a mark or 1 in each data bit. Or vice versa if A pair is selected. Since the right audio signal encoder has the same configuration as the left audio signal encoder, with particular reference to FIG. 3 which shows only the left audio signal encoder, if the audio signal is not converted to a digital signal, this encoder system Each audio signal is A/D
Notch filter 301.30 via converter 307
3. The digitized audio signal is also fed to a control branch of the encoder that includes a masking filter 305, the output of which is fed via a rectifier 309 to a multiplier 311, which is also fed the output of a code frequency generator 211. Ru. The output of the multiplier 311 is sent to the adder 313
The adder 313 generates the desired encoded audio signal via the D/A converter 315 if this encoder is used.

In use of this encoder system, the notch filters 301, 303 form a series of notches in the audio signal in the frequency band determined by the random sequence generator 201, each notch as described in European Patent Application No. 0245037. the appropriate code signal at the appropriate frequency as described in further detail in the literature. Masking filter 30
The control branch containing f5 specifies that the amplitude of the code signal is not determined by the amplitude of the audio signal at higher or lower frequencies, which do not adequately mask the code signal.
I'm stunned. The MAJ retoucher 311 ensures that the amplitude of the code signal can be kept at a fixed level lower than the amplitude of the audio signal.

In FIGS. 4 and 5, three decoders 401, 403,
405, each decoder being responsive to one of the possible combinations of the pair of notch frequency bands A, B, C. Each decoder 401, 403, 405 is identical and has the configuration shown in FIG. Especially with reference to Figure 5,
The encoded stereo signal of each channel is individually filtered within each decoder 401.403.405 by a first bandpass filter 501.502 which serves to separate the code frequency from the stereo signal. Automatic gain control units 503, 504 adjust the amplitude of the code signal to a constant level. The difference between the outputs of units 503 and 504 is obtained in a subtractor 505 to generate a signal prefixed to 32 bits of code 271
3Hz space data bit signal and 3228H
The mark data bit signals of z are separated by appropriate bandpass filters 507.509 and rectifiers 511.
513. The bandwidth of filters 507, 509 is generally wider than the notch formed in the audio signal to allow for speed variations in the playback device.

This represents a program breakthrough for code demodulation.
hl, and occasional code erasures occur, but this is overcome by the combination of complementary code sequences generated in adder 515 and subtracter 517 by rectifiers 511 and 513. Therefore, a program breakthrough is detectable and compensable since the output of subtractor 517 generates a double amplitude code signal along with the output of adder 515 which would be zero in the absence of a program breakthrough. .

Referring again to FIG. 4, three decoders 401 and 40
The output of 3,405 is monitored by suitable code recognition means 407, and when a valid code signal occurs it is identified and displayed on a suitable code display means, such as a display (VDU) or printer. The code recognition means 407 is also effective in detecting and compensating for program breakthroughs. Generally, the output from the decoder system is examined by code recognition means 407 to check whether the expected pattern of code sequences is present or an attempt is made to remove the code.

This decoder system uses high-speed DSP integrated circuits to generate 2
The decoding of several notches within one DSP chip must decode signals from all possible combinations of two notches, but in response to the same coded signal input, but considering different notch combinations.・It is possible to operate the unit. This decoder is designed to examine all possible notch combinations simultaneously.
By operating the system, this decoder system generates a random sequence generator 201
does not require any knowledge of the sequence in the notch frequencies generated by. However, the provision of such knowledge allows for simplification of the decoder system.

In the signal coding system according to the embodiments described above,
The three possible combinations of notch frequencies are A, B, and C.
However, in practice a larger number of combinations may be used, even though this results in a more complex decoder system. However, the encoder 209 using a DSP chip
In this case, only two notch filters 301, 301 and one masking filter 305 are required for one channel of the audio signal. Thus, any combination of notch frequencies can be created simply by executing software. However, although there are great benefits in having the system according to the invention in digital form, it is also possible to have an analog form of the system.

Systems according to the invention may incorporate more advanced technology. FIG. 6 shows an example of a more sophisticated encoder. In FIG. 6, encoders and decoders corresponding to the encoder of FIG. 3 and the decoder of FIG. 5 are indicated by the same reference numerals, and both left and right stereo channels are shown. The encoder shown in FIG. Code truncation means are provided to serve to prevent insertions.The encoder is therefore equipped with delay units 611, 613, 61, which serve to introduce a delay of, for example, approximately 1 second into the audio signal.
It is equipped with 5,617.

This delay is achieved by bandpass filters 507, 509, rectifiers 511, 513, and adders and subtracters 505, 515 set to appropriate upper and lower notch frequency bands, respectively.
A decoder section 517 enables a level check section 619 to monitor the audio signal originating from the left and right notched input signals. Automatic gain control unit 503 for each channel
．． 504 are provided which constantly vary the gain of the masked music signal system such that the code remains at a constant level if the music signal system is well coded. Level check section 619 ensures that codes are not inserted if their amplitude is unrecoverably low in a particular section of the audio signal. Interference from the audio signal is also checked to ensure that the code is not significantly corrupted. Code generator 211 generates a complete code if the audio signal is suitable for the duration of one sequence.
It is responsive to an enable signal from the level check system to generate the sequence. When one chord sequence ends, the beginning of the same sequence is delayed.
Originates from unit 611.613.615.617. The coded signal is then sent to code generator 2
Cross fade unit 619.6 under the control of 11
12 to the output for the duration of the code sequence.

Although it is particularly advantageous to insert each code signal at two different frequencies relative to the input signal, the present invention provides a method for inserting each code signal at a single frequency, as described, for example, in U.S. Pat. No. 3,845,391. It is also applicable to signal coding systems configured to be inserted into a signal.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the six possible notch frequencies selected within a stereo music recording signal; FIG. 2 is a block diagram illustrating an encoder for the present system; FIG. FIG. 4 is a block diagram of a decoder; FIG. 5 is a detailed diagram of one of the decoders shown in FIG. 4; and FIG. 6 is a modification of the encoder shown in FIG. It is a block diagram. 201...Random sequence generator 207...Filter coefficient storage 209...
... Encoder 211 ... Code generator 301.30
3...Notch filter 305...Masking filter 307...A/D converter 311...Multiplier 315...D/A converter

Claims (1)

[Claims] 1. Encoding means comprising means for selecting a variable sequence of frequency bands from a plurality of different predetermined frequency bands within the bandwidth of a given signal; and the selected frequency band. means for removing a sequence of notches from said given signal to form a corresponding sequence of notches in said given signal; A signal identification device comprising: means for inserting a sequence into the notch; and decoding means for determining in which of the given signals a code signal is present. 2. The apparatus of claim 1, wherein there are at least three different predetermined frequency bands, and each code signal has a frequency within the two different predetermined frequency bands. 3. The apparatus of claim 2, wherein the code signals within two different predetermined frequency values each represent a different binary value. 4. Apparatus as claimed in any one of claims 1 to 3, wherein said decoding means includes means for substantially simultaneously examining all possible combinations of predetermined frequency bands in the signal. 5. The variable sequence is a predetermined sequence;
5. Apparatus as claimed in any preceding claim, wherein said decoding means comprises means for examining said predetermined frequency bands in said predetermined sequence order. 6. means for selecting a variable sequence of frequency bands from a plurality of different predetermined frequency bands within the bandwidth of a given signal; and removing the selected sequence of frequency bands from said given signal. , means for forming a corresponding sequence of notches in said given signal; and means for inserting into said notch a sequence of each code signal having a frequency within the bandwidth of said notch undergoing insertion. encoding device for the coding of a given signal. 7. The apparatus of claim 6, wherein there are at least three different predetermined frequency bands, and each code signal comprises a frequency within two different predetermined frequency bands. 8. The apparatus of claim 7, wherein the code signals within two different predetermined frequency values each represent a different binary value. 9. The encoding means according to any one of claims 6 to 8, wherein the encoding means includes means for inhibiting the insertion of the code signal into the notch if the code signal appears undetectable. equipment. 10. Decoding for decoding a signal, characterized in that the code signal consists of a variable sequence of one predetermined frequency band in the signal, and includes means for examining a plurality of combinations of said predetermined frequency bands. Device.